My list starts with the £sd ‘square’ issues of 1969 which soon after transformed into the decimal 10p cerise, 20p, 50p and £1. These were lovely stamps and you felt you were getting something for your money. In 1969 I would have been earning about £14 a week so 2/6d was a lot to fork out.
Mercifully, subsequent major changes were well spaced out for a while!
Then there are the big, tall Machins in two colours. I never really liked them but the odd values like £1.33 were interesting and broke the monotony.
I have also included the Castle issues from 1988 which I know aren’t Machins but they were around for 7 years before rate had increased so much that even the £5 became small format. I grew up with the £sd Castles and must include them soon too.
These are just the larger format stamps -